Pharmacogenomics and other ?omics methods are cornerstone technologies that will drive biomarker discovery for the Personalized Medicine revolution. However, these technical advances are not yet uniformly applied, as there is under-representation in personalized medicine (PM) research that cuts across ages, genders, racial minorities, and socioeconomic groups. This is particularly true for American Indian and Alaska Native (AI/AN) populations, which are critical communities to involve in discovery research for several reasons. First, these populations have been neglected to date, partly due to a lack of community engagement and historical mistrust around the scientific enterprise. Second, these oftentimes isolated populations can have differences in the prevalence of known, function-disrupting gene variants of clinical significance and/or may possess novel variants with altered function. Third, the effects of unique dietary and other environmental influences among these AI/AN populations on drug response may be modified by genetic variation. We address these issues in Aims 1-3 of Project 2 of our Program Project grant, which seeks a better understanding of the relationship between novel measurements of short- and long-term hepatic vitamin K status, variation in vitamin K cycle genes, and warfarin anticoagulation outcomes. Warfarin is still the most commonly used drug in its pharmacological class in the US and has enormous clinical utility for AI/AN populations, who have more restricted access to emergency hospital facilities and expensive new anticoagulant medications. In Aim 1 we will develop more sensitive and specific biomarkers of hepatic vitamin K status than the existing plasma ELISA-based PIVKA-II and vitamin K assays, using LC-MS/MS-based approaches to quantitate all eleven (proteo)forms of carboxylated prothrombin (Factor II) in plasma and CYP4F2-dependent vitamin K catabolites in urine. This is biologically significant because hepatic vitamin K levels affect Factor II proteoform synthesis and several undercarboxylated proteoforms have clotting factor activity. In Aim 2, we will use our enhanced assays to (A) characterize short- and long-term hepatic vitamin K status in three AI/AN populations and test its association with CYP4F2*3 and (B) directly test whether the gene variant modifies the effect of vitamin K supplementation on hepatic vitamin K status. In Aim 3, we will test whether prospectively applied pharmacogenetic and biomarkers tests of hepatic vitamin K status are associated with long-term hemostasis control in AI/AN (and all other) populations receiving warfarin-based anticoagulation therapy. These aims are highly clinically significant. Specifically, they will enhance our understanding of the regulation of hepatic vitamin K status, and by inference all human vitamin K-dependent Gla proteins, by CYP4F2. The results may also further the development of a new decision tree for warfarin versus DOAC therapy based on the aforementioned PM test results.s.